Imaging device and imaging unit

ABSTRACT

An imaging device having a first surface on which light is incident and a second surface on an opposite side of the first surface, includes a photoelectric conversion section including semiconductors having a same conductivity type, in which an impurity concentration on the second surface side is higher than an impurity concentration on the first surface side.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a U.S. National Stage application claiming thebenefit of prior filed International Application NumberPCT/JP2013/006816, filed Nov. 20, 2013, in which the InternationalApplication claims a priority date of Nov. 22, 2012, based on priorfiled Japanese Application Number 2012-256891, the entire contents onwhich are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to an imaging device and an imaging unit.

BACKGROUND ART

In order to realize a global shutter in a CMOS (complementary metaloxide semiconductor) image sensor, there is known an imaging apparatusin which a storage section is provided to a pixel (refer to Non-PatentDocument 1, for example).

Non-Patent Document 1: Keita Yasutomi, Shinya Itoh, Shoji Kawahito, “A2.7e-Temporal Noise 99.7% Shutter Efficiency 92 dB Dynamic Range CMOSImage Sensor with Dual Global Shutter Pixel”, ITE Technical Report, Vol.34, No. 16, pp. 25-28

DISCLOSURE Problems to be Solved

The conventional technique leaves room to be improved in a point that atransfer omission of charge may occur in a photoelectric conversionsection.

Means for Solving the Problems

An imaging device as one example of the present invention having a firstsurface on which light is incident and a second surface on an oppositeside of the first surface, includes a photoelectric conversion sectionincluding semiconductors having a same conductivity type, in which animpurity concentration on the second surface side is higher than animpurity concentration on the first surface side.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a configuration example of a digitalcamera.

FIG. 2 is a diagram illustrating a pixel arrangement in an imagingdevice in a first configuration example.

FIG. 3 is an explanatory diagram of a focus detection method conductedby a pupil-division phase difference method.

FIG. 4(a) to FIG. 4(e) are explanatory diagrams of image signalgeneration processing.

FIG. 5 is a circuit diagram of an example of a pixel PX.

FIG. 6 is an enlarged plan view of a pixel array in the firstconfiguration example.

FIG. 7 is an enlarged plan view of an example of the pixel PX.

FIG. 8 is a sectional view of the pixel PX in the first configurationexample.

FIG. 9 is a sectional view of a pixel PX in a second configurationexample.

FIG. 10 is a diagram illustrating an example of a pixel array on a lightreceiving surface side in the second configuration example.

FIG. 11 is a diagram illustrating an example of a pixel array on a rearsurface side of the light receiving surface in the second configurationexample.

FIG. 12 is a graph illustrating an example of relation between a lightabsorptivity obtained by a silicon substrate and a thickness of thesilicon substrate, regarding respective wavelengths of R, G, and B.

FIG. 13 is a diagram illustrating a pixel PX when seen from a rearsurface side of a light receiving surface in a third configurationexample.

FIG. 14(a) and FIG. 14 (b) are diagrams each illustrating an example ofa stacked structure of an imaging device.

FIG. 15 is a diagram illustrating another example of a pixel arrangementas a modified example of the second configuration example.

DETAILED DESCRIPTION OF THE EMODIMENTS

Hereinafter, embodiments of the present invention will be describedwhile referring to the drawings. Note that in the following descriptionand the drawings, an X direction is defined as a horizontal direction, aY direction is defined as a vertical direction, and a Z direction isdefined as a forward and backward direction, unless otherwise noted.

<Configuration Example of Imaging Unit>

FIG. 1 is a diagram illustrating a configuration example of a digitalcamera as an example of an imaging unit. A digital camera 1 has aninterchangeable lens 2 and a camera body 3. The interchangeable lens 2is mounted on the camera body 3 via a mount part 4.

The interchangeable lens 2 includes a lens control part 5, a main lens9, a zoom lens 8, a focusing lens 7, and a diaphragm 6. The lens controlpart 5 has a microcomputer, a memory and the like. The lens control part5 performs a drive control of the focusing lens 7 and the diaphragm 6, adetection of an aperture state of the diaphragm 6, a position detectionof the zoom lens 8 and the focusing lens 7, a transmission of lensinformation with respect to a body control part 14 on the camera body 3side, which will be described later, a reception of camera informationfrom the body control part 14, and the like.

The camera body 3 includes an imaging device 12, an imaging devicedriving part 19, the body control part 14, a liquid crystal displayelement driving circuit 15, a liquid crystal display element 16, aneyepiece lens 17, an operation member 18, and the like. Further, to thecamera body 3, a memory card 20 being a nonvolatile storage medium isdetachably attached.

The imaging device 12 is arranged on a planned imaging plane of theinterchangeable lens 2, and captures an image of subject formed by theinterchangeable lens 2. Note that the imaging device 12 in the presentembodiment can receive, with the use of a pair of pixels, respectivelight fluxes which pass through different partial areas of a pupil ofthe interchangeable lens 2, and can obtain phase difference informationof the subject image when performing automatic focus (AF). Note that aconfiguration example of the imaging device 12 will be described later.

The body control part 14 has a microcomputer, a memory and the like. Thebody control part 14 performs an operation control of the entire digitalcamera. Further, the body control part 14 and the lens control part 5perform communication via an electric contact portion 13 of the mountpart 4.

The imaging device driving part 19 generates, in accordance with aninstruction from the body control part 14, an instruction signal withrespect to the imaging device 12. The liquid crystal display elementdriving circuit 15 drives the liquid crystal display element 16 inaccordance with the instruction from the body control part 14. Note thatthe liquid crystal display element 16 functions as an electronicviewfinder, and a photographing person can observe an image displayed onthe liquid crystal display element 16, through the eyepiece lens 17.

The image of subject formed on the imaging device 12 by theinterchangeable lens 2 is subjected to photoelectric conversion by theimaging device 12. Timings for storing photoelectric conversion signalsand for reading the signals (frame rates) in the imaging device 12 arecontrolled by a control signal from the imaging device driving part 19.An output signal from the imaging device 12 is converted into digitaldata by a not-illustrated A/D conversion part, and sent to the bodycontrol part 14.

The body control part 14, being one example of a focusing part,calculates a defocus amount based on the output signal, corresponding toa predetermined focus detecting area, from the imaging device 12.Subsequently, the body control part 14 sends the aforementioned defocusamount to the lens control part 5. The lens control part 5 calculates afocusing lens driving amount based on the defocus amount received fromthe body control part 14, and based on the lens driving amount, the lenscontrol part 5 drives the focusing lens 7 using a not-illustrated motoror the like to move the lens to a focus position.

Further, the body control part 14 generates recording image data basedon a signal output from the imaging device 12 after the photographinginstruction is issued. The body control part 14 stores the generatedimage data in the memory card 20. Further, the body control part 14sends the generated image data to the liquid crystal display elementdriving circuit 15, and makes the liquid crystal display element 16reproduce and display the image.

Note that the camera body 3 is provided with a shutter button, and asetting member 18 of the focus detecting area. The body control part 14detects an operation signal made by the aforementioned operation member18, and performs a control of operations (photographing processing,setting of focus detecting area, and the like) in accordance with adetection result.

<First Configuration Example of Imaging Device>

Next, a configuration example of the imaging device 12 will bedescribed. The imaging device in the present embodiment is, for example,a solid-state imaging device of XY address type formed on a siliconsubstrate by using a CMOS (complementary metal oxide semiconductor)process.

FIG. 2 is a diagram illustrating a pixel arrangement in an imagingdevice in a first configuration example. An imaging device 12 aillustrated in FIG. 2 has a pixel part 31 in which a plurality of pixels(PX) each converting incident light into an electrical signal arearrayed, a vertical scanning part 32, and a horizontal scanning part 33.Note that in the drawing, the array of pixels PX is illustrated in asimplified manner, but, it is needless to say that a larger number ofpixels are arrayed on a light receiving surface of an actual imagingdevice.

The vertical scanning part 32 is one example of a control part, and, forexample, it supplies various types of control signals to the pixel part31 and the horizontal scanning part 33, upon receiving an instructionsignal from the imaging device driving part 19. To the vertical scanningpart 32, a plurality of horizontal signal lines extending in a rowdirection (X direction) are connected. The vertical scanning part 32supplies the control signal to the respective pixels via the horizontalsignal lines. Note that the illustration of the horizontal signal linesis omitted in FIG. 2. Note that the control signal which is supplied tothe pixel PX may also be generated by the imaging device driving part 19of the digital camera 1.

To the horizontal scanning part 33, a plurality of vertical signal linesextending in a column direction (Y direction) are connected. Thehorizontal scanning part 33 reads output signals of the respectivepixels via the vertical signal lines. Note that the illustration of thevertical signal lines is omitted in FIG. 2.

Further, as illustrated in FIG. 2, the pixel PX in the pixel part 31 hasa square shape, and is arranged in a state where each side thereof isrotated by 45 degrees with respect to the row direction and the columndirection. Further, the respective pixels are densely arrayed so thatrespective sides of each pixel are brought into contact with neighboringpixels. Therefore, in the pixel part 31, pixels on an odd number row andpixels on an even number row are arranged by being displaced by halfpitch, and pixels on an odd number column and pixels on an even numbercolumn are arranged by being displaced by half pitch.

A half area of the pixel PX is covered by a lightproof film, forexample, so that the pixel PX shields a light flux which passes througha partial area of a pupil of an optical system. Further, on an openingof the pixel PX which is not covered by the lightproof film, aphotoelectric conversion section is arranged. In the drawing, the areacovered by the lightproof film (pupil-division lightproof section MS) isillustrated by hatching.

Further, on a front surface of the pixel PX, a microlens MLN and anoptical filter (color filter) are arranged. Further, on a lightreceiving surface of the imaging device, an infrared cut filter (notillustrated) which inhibits a passage of infrared light is arranged at aposition in front of the microlens MLN and the optical filter (onincident side of light). The color filters of the pixels PX havedifferent spectral sensitivities according to pixel positions. For thisreason, the pixel PX outputs an electrical signal corresponding to eachcolor, through a color separation in the color filter. Note that in thedrawing, a color of the color filter corresponding to the pixel PX isindicated by a symbol.

If attention is focused on the row direction (X direction) of the pixelpart 31, on the odd number rows in the pixel part 31, G pixels eachreceiving light of green (G) component are arranged along the Xdirection. On the even number rows in the pixel part 31, B pixels eachreceiving light of blue (B) component and R pixels each receiving lightof red (R) component are alternately arranged along the X direction.

Further, if attention is focused on the column direction (Y direction)of the pixel part 31, although the G pixels are arranged along the Ydirection on the odd number columns in the pixel part 31, on the evennumber columns in the pixel part 31, the column on which the B pixelsare arranged along the Y direction and the column on which the R pixelsare arranged along the Y direction, are alternately arrayed.

Regarding the G pixels, the pixel whose left half is opened and thepixel whose right half is opened, are alternately arranged in each ofthe row direction (X direction) and the column direction (Y direction).Further, regarding the B pixels and the R pixels, the pixel whose upperhalf is opened and the pixel whose lower half is opened, are alternatelyarranged in the column direction (Y direction). Note that in the rowdirection (X direction), the B pixels and the R pixels are arranged in amanner that the position of the opening of the B pixel and the positionof the opening of the R pixel become opposite to each other, on the sameeven number row.

By the above-described arrangement, in the row direction (X direction),the G pixel whose left half is opened (one example of first pixel) andthe G pixel whose right half is opened (one example of second pixel)make a set in a bilaterally symmetric state, and the sets are arrangedone by one. Specifically, on the row on which the G pixels are arranged,a photoelectric conversion section of the first pixel, a lightproofsection MS of the first pixel, a lightproof section MS of the secondpixel, and a photoelectric conversion section of the second pixel arearranged in this order, when seen from the left side in the X direction.Further, in the X direction, a photoelectric conversion section of the Gpixel whose left half is opened, which is different from the first pixel(one example of fifth pixel), is arranged at a position adjacent to thephotoelectric conversion section of the second pixel. Note that aconfiguration of the first pixel and a configuration of the fifth pixelare the same.

Therefore, an image of a left half of an exit pupil and an image of aright half of the exit pupil can be obtained by the pair of G pixelsarranged to face each other in the horizontal direction (the secondpixel and the fifth pixel, in the aforementioned example). Specifically,phase difference information in the horizontal direction of a subjectimage used in the phase difference AF can be obtained by the pair of Gpixels.

Further, in the column direction (Y direction), the B pixel whose upperhalf is opened (one example of third pixel) and the B pixel whose lowerhalf is opened (one example of fourth pixel) make a set in a verticallysymmetric state, and the sets are arranged one by one. Specifically, onthe column on which the B pixels are arranged, a photoelectricconversion section of the third pixel, a lightproof section MS of thethird pixel, a lightproof section MS of the fourth pixel, and aphotoelectric conversion section of the fourth pixel are arranged inthis order, when seen from the upper side in the Y direction. Further,in the Y direction, a photoelectric conversion section of the B pixelwhose upper half is opened, which is different from the third pixel (oneexample of sixth pixel), is arranged at a position adjacent to thephotoelectric conversion section of the fourth pixel.

In like manner, in the column direction (Y direction), the R pixel whoseupper half is opened (one example of third pixel) and the R pixel whoselower half is opened (one example of fourth pixel) make a set in avertically symmetric state, and the sets are arranged one by one.Specifically, on the column on which the R pixels are arranged, aphotoelectric conversion section of the third pixel, a lightproofsection MS of the third pixel, a lightproof section MS of the fourthpixel, and a photoelectric conversion section of the fourth pixel arearranged in this order, when seen from the upper side in the Ydirection. Further, in the Y direction, a photoelectric conversionsection of the R pixel whose upper half is opened, which is differentfrom the third pixel (one example of sixth pixel), is arranged at aposition adjacent to the photoelectric conversion section of the fourthpixel. Note that in each of the examples of the B pixels and the Rpixels, a configuration of the third pixel and a configuration of thesixth pixel are the same.

Therefore, an image of a lower half of the exit pupil and an image of anupper half of the exit pupil can be obtained by the pair of B pixels orthe pair of R pixels arranged to face each other in the verticaldirection (the fourth pixel and the sixth pixel, in the aforementionedexample). Specifically, phase difference information in the verticaldirection of the subject image used in the phase difference AF can beobtained by the pair of B pixels or the pair of R pixels. As describedabove, the imaging device 12 a of the first configuration example canalso be considered as an imaging device in which the focus detectingpixels are arranged on the whole surface of the light receiving surface.

Note that in the pixel part 31, a pair of G pixels on the odd numberrow, and a pair of B pixels or a pair of R pixels on the even numbercolumn are arranged so that four openings (photoelectric conversionsections) thereof form a square. In like manner, in the pixel part 31, apair of G pixels on the odd number row, and a pair of B pixels or a pairof R pixels on the even number column are arranged so that fourlightproof sections thereof form a square. Note that when looking at thepixel part 31 as a whole, the square-shaped openings each formed by fourpixels and the square-shaped lightproof sections each formed by fourpixels are arrayed so as to form a checkered pattern. Further, in thepixel part 31, the lightproof sections each formed by four pixels mayalso be integrally formed.

Here, focus detection processing based on phase difference informationobtained from the imaging device 12 a, will be described. Hereinafter,description will be made by citing the G pixel whose left half is openedand the G pixel whose right half is opened, as an example, but, thefocus detection using the R pixels and the B pixels is also conductedbased on a similar principle.

As illustrated in FIG. 3, a light flux A which passes through a firstarea 201 of an exit pupil 200 of the interchangeable lens 2 is incidenton G pixels 21 in each of which a right half is opened, and a light fluxB which passes through a second area 202 of the exit pupil 200 isincident on G pixels 22 in each of which a left half is opened.

An in-focus state is a state where a sharp image is formed on theimaging device 12 a, so that a pair of images formed by thepupil-divided light fluxes match on the imaging device 12 a, asdescribed above.

On the other hand, an out-of-focus state is a state where a sharp imageis formed at a position in front of the imaging device 12 a, or at arear side of the imaging device 12 a, so that the pair of images formedby the pupil-divided light fluxes do not match on the imaging device 12a. In this case, signal waveforms obtained from the G pixels 21 and theG pixels 22 have mutually different positional relationships (an imagedeviation direction and an image deviation amount), in accordance with adeviation from the in-focus state (defocus amount).

Accordingly, the body control part 14 of the digital camera 1 is onlyrequired to calculate the defocus amount based on the positionalrelationships of the signal waveforms obtained from the G pixels 21 andthe G pixels 22. The calculated defocus amount is transmitted to thelens control part 5 as camera information. Further, when the lenscontrol part 5 makes the focusing lens 7 perform forward/backwardmovement in an optical axis direction based on the camera information, afocal position of the interchangeable lens 2 is adjusted so that a sharpimage is formed on the imaging device 12 a.

Next, image signal generation processing for generating a color imagesignal based on an output signal from the imaging device 12 a, will bedescribed while referring to FIG. 4(a) to FIG. 4(e).

In the image signal generation processing, the vertical scanning part 32of the imaging device 12 a reads a pair of G pixels whose photoelectricconversion sections are adjacent in the X direction (the second pixeland the fifth pixel, in the above-described example) by performinghorizontal addition on the pixels, to thereby generate a G image signal.FIG. 4(a) illustrates a state where the horizontal addition is performedon the G pixels, and FIG. 4(b) illustrates sampling positions of the Gimage signals generated through the horizontal addition.

Further, the vertical scanning part 32 reads a pair of B pixels whosephotoelectric conversion sections are adjacent in the Y direction (thefourth pixel and the sixth pixel, in the above-described example) byperforming vertical addition on the pixels, to thereby generate a Bimage signal. In like manner, the vertical scanning part 32 reads a pairof R pixels whose photoelectric conversion sections are adjacent in theY direction (the fourth pixel and the sixth pixel, in theabove-described example) by performing vertical addition on the pixels,to thereby generate an R image signal. FIG. 4(c) illustrates a statewhere the vertical addition is performed on the B pixels and the Rpixels, and FIG. 4(d) illustrates sampling positions of the B imagesignals and the R image signals generated through the vertical addition.

FIG. 4(e) illustrates an image as a result of synthesizing the G imagesignals generated through the horizontal addition, and the B imagesignals and the R image signals generated through the vertical addition.The body control part 14 of the digital camera 1 can obtain an image inBayer array, by synthesizing the G image signals, the B image signals,and the R image signals. Note that the image in FIG. 4(e) has a pixelpitch which is about 1.4 times (√2 times) a pixel pitch beforeperforming the addition, and has a number of pixels which is half anumber of pixels before performing the addition.

Further, the body control part 14 performs color interpolationprocessing on the above-described image in Bayer array (FIG. 4(e)), tothereby generate image signals of lacked color components. The colorinterpolation processing in the Bayer array is publicly-known, so thatdetailed explanation thereof will be omitted. As a result of such colorinterpolation processing, color image signals (RGB) are obtained. Thebody control part 14 generates, for example, a recording image file byusing the color image signals, and records the file in the memory card20.

Subsequently, a configuration of each pixel PX in the firstconfiguration example will be described in detail. FIG. 5 is a circuitdiagram of an example of the pixel PX.

The pixel PX has a photodiode PD, a first reset transistor RST1, a firstglobal switch transistor GS1, a storage diode SD, a transfer transistorTX, a second global switch transistor GS2, a second reset transistorRST2, an amplifying transistor AMP, a selection transistor SEL, and afloating diffusion part FD.

The photodiode PD is an example of a photoelectric conversion section,and generates a signal charge through photoelectric conversion inaccordance with a light intensity of incident light.

The first reset transistor RST1 has a source connected to the photodiodePD, and a drain connected to a power supply voltage VDD. For example,the first reset transistor RST1 is turned on during a period of time inwhich a signal φRST1 applied to a gate thereof is at a high level, toreset a charge in the photodiode PD.

The first global switch transistor GS1 has a source connected to thephotodiode PD, and a drain connected to the storage diode SD. Forexample, the first global switch transistor GS1 is turned on during aperiod of time in which a signal φGS1 applied to a gate thereof is at ahigh level, to transfer the signal charge stored in the photodiode PD tothe storage diode SD.

The storage diode SD is an example of a storage section, and has apotential well for storing the charge transferred from the photodiodePD. The storage diode SD is formed by a MOS structure, for example, andthe storage diode SD is designed to be able to store charges whoseamount is larger than an amount of charges stored in the photodiode PD.

The transfer transistor TX has a source connected to the storage diodeSD, and a drain connected to the floating diffusion part FD. Forexample, the transfer transistor TX is turned on during a period of timein which a signal φTX applied to a gate thereof is at a high level, totransfer the signal charge stored in the storage diode SD to thefloating diffusion part FD.

The second global switch transistor GS2 has a source connected to thephotodiode PD, and a drain connected to the floating diffusion part FD.For example, the second global switch transistor GS2 is turned on duringa period of time in which a signal φGS2 applied to a gate thereof is ata high level, to transfer the signal charge stored in the photodiode PDto the floating diffusion part FD.

The floating diffusion part FD corresponds to a region in which aparasitic capacitor storing the charge transferred from the photodiodePD or the storage diode SD is formed. The floating diffusion part FDcorresponds to, for example, a diffusion region formed by introducingimpurities into a semiconductor substrate.

The second reset transistor RST2 has a source connected to a gate of theamplifying transistor AMP, and a drain connected to the power supplyvoltage VDD. For example, the second reset transistor RST2 is turned onduring a period of time in which a signal φRST2 applied to a gatethereof is at a high level, to reset the charge in the floatingdiffusion part FD.

The amplifying transistor AMP has a drain and a gate connected to thepower supply voltage VDD and the floating diffusion part FD,respectively, and a source connected to a drain of the selectiontransistor SEL, and forms a source follower circuit in which a constantcurrent source IS connected to the vertical signal line VL is set to aload. The amplifying transistor AMP outputs a read current via theselection transistor SEL, in accordance with a voltage value of thefloating diffusion part FD.

Further, the selection transistor SEL is turned on during a period oftime in which a signal φSEL applied to a gate thereof is at a highlevel, to connect the source of the amplifying transistor AMP to thevertical signal line VL.

Here, components of each of the above-described first pixel to sixthpixel are the same. Accordingly, each of the first pixel to the sixthpixel basically has the photodiode PD, the first reset transistor RST1,the first global switch transistor GS1, the storage diode SD, thetransfer transistor TX, the second global switch transistor GS2, thesecond reset transistor RST2, the amplifying transistor AMP, theselection transistor SEL, and the floating diffusion part FD. Further,although FIG. 5 illustrates only the circuit configuration of one pixel,for example, the second reset transistor RST2, the amplifying transistorAMP, and the selection transistor SEL may also be shared by a pluralityof pixels.

Further, FIG. 6 is an enlarged plan view of the pixel array of the pixelpart 31 illustrated in FIG. 2. FIG. 7 is an enlarged plan view of anexample of the pixel PX.

On an opening of the pixel PX, on the light receiving surface side ofthe imaging device 12 a, there are arranged the photodiode PD formed tohave an approximately trapezoidal shape, and the first reset transistorRST1. On the lightproof section of the pixel PX, there are arranged thefirst global switch transistor GS1, the storage diode SD, the transfertransistor TX, and the second global switch transistor GS2. Note that areference numeral 23 in FIG. 6 indicates a circuit in which theamplifying transistor AMP and the selection transistor SEL shared byfour pixels are integrated. Note that a reference numeral 24 in FIG. 6indicates the second reset transistor RST2 shared by two pixels.Further, in FIG. 6 and FIG. 7, an area of the photodiode PD on the lightreceiving surface is set to be larger than an area of the storage diodeSD.

As illustrated in FIG. 6, each of the R pixel, the G pixel, and the Bpixel has the same circuit configuration. The circuits of the G pixelsadjacent in the row direction (X direction) are arranged in abilaterally symmetric state on the light receiving surface. Further, thecircuits of the B pixels and the circuits of the R pixels adjacent inthe column direction (Y direction) are respectively arranged in avertically symmetric state on the light receiving surface.

Further, FIG. 8 is a sectional view of the pixel PX in the firstconfiguration example. Note that in FIG. 8, illustration of wiring andthe like is omitted. For example, the photodiode PD has an n-typesemiconductor region n1 formed on a light receiving surface side of ap-type semiconductor substrate SUB (upper side in FIG. 8). Further, thestorage diode SD has an n-type semiconductor region n2 formed on thelight receiving surface side of the p-type semiconductor substrate SUB.

Further, on a lower layer of the semiconductor region n2 of the storagediode SD, a p-type shield layer (p2) is formed by being stacked on thelayer. The shield layer is formed so as to cover the entire region ofthe semiconductor region n2, and is formed so as to be brought intocontact with a later-described separating section IS according to need.Further, the first global switch transistor GS1 is formed between thephotodiode PD and the storage diode SD.

Further, an impurity concentration of the semiconductor region n1 of thephotodiode PD and an impurity concentration of the semiconductor regionn2 of the storage diode SD are different to each other. For example, theimpurity concentrations of the regions n1 and n2 are respectively set sothat a potential of the storage diode SD is positioned between apotential of the photodiode PD and a potential of the floating diffusionpart FD, when the first global switch transistor GS1 is at a low level.

Further, the separating section IS formed in the semiconductor substrateSUB is, for example, a p-type well for insulating and separating pixelswhich are adjacent to each other. Note that at a position among thestorage diode SD, the separating section IS, and the shield layer (p2),a p-type region 36 is formed. Further, in a gate layer GLY provided onthe semiconductor substrate SUB, there are formed the first resettransistor RST1, the first global switch transistor GS1, the transfertransistor TX, a gate electrode of the second global switch transistorGS2 which is not illustrated in FIG. 8, and the like. Note that theconductivity type of the semiconductor described in the firstconfiguration example is only one example.

Further, on the gate layer GLY of the semiconductor substrate SUB, awiring layer MLY including the lightproof section MS is provided. Forexample, the lightproof section MS is formed by a metal film or thelike. The lightproof section MS is arranged so as to cover a region inwhich the first global switch transistor GS1, the storage diode SD, thetransfer transistor TX, and the second global switch transistor GS2 arearranged. Specifically, on the photodiode PD, there is formed an openingin which the lightproof section MS does not exist.

Here, in the pixel PX, the lightproof section MS is formed by a singlemember, and has a function as a pupil-division lightproof section and afunction as a lightproof section for storage section which shieldsincident light with respect to the storage diode SD. Note that thelightproof section MS may be formed at a place other than the lowermostlayer of the wiring layer MLY, or it may also be formed at a place wherea wiring is provided. For example, the wiring may be formed in a layerdifferent from the layer in which the lightproof section MS is provided,or it may also be formed in a layer same as the layer in which thelightproof section MS is provided.

Further, on the wiring layer MLY, an optical filter OFL which functionsas a color filter is arranged. On the optical filter OFL, a flat layerPLY is formed. Further, on the flat layer PLY, the microlens MLN isarranged.

Further, in each of the pixels including the first pixel to the sixthpixel described above, a center of optical axis of the microlens MLN ispositioned by being aligned with a boundary between the lightproofsection MS and the opening (photoelectric conversion section), in orderto perform the pupil division.

Further, description will be made on operation modes when reading asignal from each pixel PX in the first configuration example. Theabove-described pixel PX has the two global switch transistors GS1 andGS2, so that it can be driven by two operation modes of a single shutterand a dual shutter.

In the operation of single shutter, the global switch transistors GS2are set to be turned off all the time. First, at a beginning of a frame,a signal charge is transferred from the photodiode PD to the storagediode SD via the global switch transistor GS1, in each of all of thepixels at the same time, as initial-stage charge transfer. This makes itpossible to realize a global electronic shutter function. Next, in eachof all of the pixels, the first reset transistor RST1 is turned on, toset the photodiode PD to be in a reset state until when a storage of thenext frame is started. By the above-described adjustment of reset time,the imaging device 12 a can freely set an exposure time (shutter speed).

Further, a signal reading operation from each pixel PX is conducted foreach row selected by the vertical scanning part 32. When the verticalscanning part 32 sets a signal φSEL(i) for i-th row to a high level,each pixel PX on the i-th row is selected. Further, when the verticalscanning part 32 sets a signal φRST1(i) for the i-th row to a highlevel, the floating diffusion part FD of each pixel PX on the i-th rowis reset. A reset voltage including the reset noise is read, as areference voltage, from each pixel PX on the i-th row. Thereafter, whenthe vertical scanning part 32 sets a signal φTX(i) for the i-th row to ahigh level, the charge in the storage diode SD is transferred to thefloating diffusion part FD by the transfer transistor TX in each pixelPX on the i-th row. This makes it possible to read the changed voltageas a signal voltage. Further, a difference between the above-describedreference voltage and the signal voltage is read, as an output signal ofeach pixel PX, by a CDS circuit (not illustrated) provided to a columnof the horizontal scanning part 33. Consequently, it is possible tocancel the reset noise and a fixed pattern noise from the output signalof each pixel PX.

Meanwhile, in the operation of dual shutter, signals stored in thestorage diodes SD and signals stored in the floating diffusion parts FDare used to obtain two images, within an imaging period of one frame.

In the operation of dual shutter, the photodiode PD is reset after theinitial-stage charge transfer, and then a charge is stored again in thephotodiode PD. The second signal charge stored after the reset istransferred to the floating diffusion part FD via the global switchtransistor GS2. The storage of the second signal charge described aboveis also conducted in each of all of the pixels at the same time, therebyrealizing the global electronic shutter. The above-described secondsignal charge is held in the floating diffusion part FD until when therow selection is performed, and when the row selection is performed, thecharge is read from each pixel PX. Further, it is only required that thefloating diffusion part FD is once reset, and then the charge in thestorage diode SD is read by being transferred to the floating diffusionpart FD by the transfer transistor TX. In the operation of dual shutter,a mere double sampling with no correlation is performed, in whichalthough the fixed pattern noise is canceled, the reset noise is notcanceled.

By using the two images obtained by the operation of dual shutterdescribed above, it is possible to realize, for example, widening ofdynamic range, a motion detection based on a difference image, acontinuous high-speed capturing of two pieces of images, and the like.

As an example, if the widening of dynamic range is performed, long-timeexposure signals are first stored in the storage diodes SD, and next,short-time exposure signals are stored in the floating diffusion partsFD. Further, it is only required to assign the long-time exposuresignals to a low-illuminance region in an image, and to assign theshort-time exposure signals to a high-illuminance region in the image,to synthesize the images. The long-time exposure signal has a low noise,and in addition to that, since a shot noise is dominant on thehigh-illuminance side, a reset noise included in the short-time exposuresignal can be ignored. Accordingly, by synthesizing the images obtainedby the operation of dual shutter, it is possible to effectively widenthe dynamic range.

Further, in the operation of dual shutter, it is possible to remarkablyshorten a difference in storage time between two pieces of images. Forexample, if the above-described widening of dynamic range is performed,it becomes easy to suppress an image strain and a motion blur whenperforming the synthesis.

Hereinafter, operations and effects of the imaging device 12 a in thefirst configuration example will be described.

(1) In the imaging device 12 a in the first configuration example, thepairs of pixels, each pair obtaining a pair of images through pupildivision, are arranged on the entire light receiving surface.Accordingly, it becomes possible to perform the focus detection based onthe phase difference AF, in the entire light receiving surface of theimaging device 12 a. Further, the respective pixels of the imagingdevice 12 a function as both imaging pixels and focus detecting pixels,so that the number of focus detecting pixels becomes very large, whencompared to a case where the focus detecting pixels are arranged on apart of the light receiving surface, resulting in that the focusdetection accuracy in the phase difference AF is improved.

(2) The imaging device 12 a in the first configuration example canobtain the phase difference information in the horizontal direction ofthe subject image, from the pair of G pixels arranged to face each otherin the horizontal direction. Further, the imaging device 12 a can obtainthe phase difference information in the vertical direction of thesubject image, from the pair of B pixels or the pair of R pixelsarranged to face each other in the vertical direction. Accordingly, theimaging device 12 a can deal with both of the phase difference AF in thehorizontal direction and the phase difference AF in the verticaldirection, resulting in that the focus detection accuracy in the phasedifference AF is improved.

(3) The imaging device 12 a in the first configuration example canobtain the phase difference information of the subject image by any ofthe R pixels, the G pixels, and the B pixels. Accordingly, the loweringof detection accuracy of the phase difference information due to a colorof the subject, becomes difficult to occur in the imaging device 12 a.Specifically, the number of subjects or scenes on which the imagingdevice 12 a has trouble performing processing, when the phase differenceAF is conducted, is reduced, resulting in that the focus detectionaccuracy in the phase difference AF is improved.

(4) The imaging device 12 a in the first configuration example canobtain the image having the Bayer array structure through the horizontaladdition of the G pixels, and the vertical addition of the B pixels andthe R pixels (refer to FIG. 4(a) to FIG. 4(e)). Accordingly, the imagingdevice 12 a can obtain a recording color image without performingspecial pixel interpolation such as one performed when the focusdetecting pixels are arranged on a part of the light receiving surface.

(5) The imaging device 12 a in the first configuration example has therespective pixels each including the photodiode PD, and the storagediode SD. By transferring the signal charge from the photodiode PD tothe storage diode SD in each of all of the pixels at the same time, theimaging device 12 a can perform the imaging using the global electronicshutter. For example, in the imaging using the global electronicshutter, a simultaneity is realized in all of the pixels, so that animage with small focal plane distortion can be obtained. Further, whenthe global electronic shutter is used at a time of performing a flashphotographing using a lighting device, even if a shutter speed is high,it becomes easy to perform synchronization between the shutter speed andthe light emission in the light device (high-speed flashsynchronization).

<Second Configuration Example of Imaging Device>

An imaging device 12 b in a second configuration example is a rearsurface irradiation type imaging device having a pixel array same asthat of the first configuration example, and in which the gate layer GLYand the wiring layer MLY are formed on a rear surface side of a lightreceiving surface thereof. The imaging device 12 b in the secondconfiguration example corresponds to a modified example of the imagingdevice 12 a in the first configuration example, in which a part, of thesecond configuration example, common to that of the first configurationexample is denoted by the same reference numeral, and overlappedexplanation thereof will be omitted.

FIG. 9 is a sectional view of the pixel PX in the second configurationexample. FIG. 9 corresponds to FIG. 8 in the first configurationexample. Further, FIG. 10 is a diagram illustrating an example of apixel array on the light receiving surface (first surface) side in thesecond configuration example. Further, FIG. 11 is a diagram illustratingan example of a pixel array on the side of the rear surface of the lightreceiving surface (second surface) in the second configuration example.

On each pixel PX on the first surface of the imaging device 12 b, themicrolens MLN, the color filter (optical filter OFL), and the lightproofsection MS formed of the lightproof film are respectively arranged.Further, on the light receiving surface of each pixel PX in the imagingdevice 12 b, visible light in accordance with the spectral sensitivityof the color filter, out of light passed through the infrared cut filter(not illustrated) which is arranged at a position in front of themicrolens MLN, is incident. Note that in the second configurationexample, the arrangement pattern of the color filter and the lightproofsection on the light receiving surface is similar to that of the firstconfiguration example.

Specifically, the lightproof section MS in the second configurationexample is arranged so as to shield a light flux which passes through ahalf part of the pupil of the optical system, and on the first surfaceof the imaging device 12 b, there are formed openings in each of whichthe lightproof section MS does not exist. The lightproof section MS isarranged so as to cover the region in which the first global switchtransistor GS1, the storage diode SD, the transfer transistor TX, andthe second global switch transistor GS2 are arranged, for example. Notethat the lightproof section MS blocks the incident of light on theadjacent pixel, so that a crosstalk of signals can be prevented.

Further, on the lightproof section MS, the optical filter OFL whichfunctions as the color filter is arranged. On the optical filter OFL,the flat layer PLY is formed. Further, on the flat layer PLY, themicrolens MLN is arranged. The center of optical axis of the microlensMLN of each pixel is positioned so as to be aligned with a boundarybetween the lightproof section MS and the opening (photoelectricconversion section), in order to perform the pupil division.

Meanwhile, on the second surface of the imaging device 12 b, the gatelayer GLY and the wiring layer MLY are formed, as described above.Further, on the second surface of the imaging device 12 b, thephotodiode PD formed to have an approximately trapezoidal shape, thefirst reset transistor RST1, the first global switch transistor GS1, thestorage diode SD, the transfer transistor TX, and the second globalswitch transistor GS2 are arranged on each pixel PX. Further, on thesecond surface of the imaging device 12 b, circuits 23 and 24 shared bypixels are also arranged.

Also in the second configuration example, each of the R pixel, the Gpixel, and the B pixel has the same circuit configuration. The circuitsof the G pixels adjacent in the row direction (X direction) are arrangedin a bilaterally symmetric state on the second surface. Further, thecircuits of the B pixels and the circuits of the R pixels adjacent inthe column direction (Y direction) are respectively arranged in avertically symmetric state on the second surface. Further, also in thesecond configuration example, an area of the photodiode PD on the secondsurface is set to be larger than an area of the storage diode SD.

Further, as illustrated in FIG. 9, an n-type semiconductor substrate SUBis used as the imaging device 12 b in the second configuration example.On a first surface of the semiconductor substrate SUB, a p-typesemiconductor layer 34 (one example of first semiconductor section) isformed. For example, the p-type semiconductor layer 34 is formed so asto cover the separating section IS and the first surface side of thepixel PX. Further, on the p-type semiconductor layer 34, the lightproofsection MS, the optical filter OFL, the flat layer PLY, and themicrolens MLN are respectively formed.

Further, the photodiode PD has the n-type semiconductor region n1 formedon a second surface side of the n-type semiconductor substrate SUB(lower side in FIG. 9). The semiconductor region n1 illustrated in FIG.9 is brought into contact with the n-type semiconductor substrate SUB.

Further, the storage diode SD has the n-type semiconductor region n2formed on the second surface side of the n-type semiconductor substrateSUB. Further, on an upper layer of the semiconductor region n2 of thestorage diode SD, the p-type shield layer (p2) is formed by beingstacked on the layer. The shield layer, being one example of aninsulation section, is formed so as to cover the entire region of thesemiconductor region n2, and is formed so as to be brought into contactwith the later-described separating section IS according to need.Further, the first global switch transistor GS1 as one example of atransfer gate section is formed between the photodiode PD and thestorage diode SD.

Further, on the second surface of the semiconductor substrate SUB,p-type semiconductor layers p+ (one example of second semiconductorsection) corresponding to the semiconductor regions n1 and n2 arerespectively formed. Further, on the second surface of the semiconductorsubstrate SUB, a p-type region 35 is formed between the substrate andthe gate layer GLY.

In each pixel PX in the second configuration example, the n-typesemiconductor substrate SUB receives, from its first surface side, apart of light flux being subjected to the pupil division by thelightproof section MS, and generates a charge through photoelectricconversion. In the imaging device 12 b in the second configurationexample, light with a long wavelength is cut by the infrared cut filter,and thus is not incident on the semiconductor substrate SUB. Further, ifthe semiconductor substrate SUB has a sufficient thickness, thephotoelectric conversion occurs in the semiconductor substrate SUB. Forexample, the thickness of the semiconductor substrate SUB (a length in adirection orthogonal to the first surface) in the second configurationexample is set to 3 μm or more.

FIG. 12 is a graph illustrating an example of relation between a lightabsorptivity obtained by a silicon substrate and a thickness of thesilicon substrate, regarding respective wavelengths of R, G, and B. Avertical axis in FIG. 12 indicates the light absorptivity in the siliconsubstrate, and a horizontal axis in FIG. 12 indicates the thickness (Sidepth) of the silicon substrate. In the example of FIG. 12, a wavelengthof B is 500 nm, a wavelength of G is 600 nm, and a wavelength of R is750 nm. The longer the wavelength of light becomes, the greater thethickness of the silicon substrate required for absorbing 50% of lightbecomes, and with respect to the wavelength of R in FIG. 12, thethickness of the silicon substrate becomes about 3.2 μm. Although thewavelength of R is set to 750 nm in FIG. 12, a peak of a sensitivityregion of R is in the vicinity of 650 nm. In the peak of the sensitivityregion of R, the thickness of the silicon substrate required forabsorbing the 50% of light becomes less than about 3.2 μm. Therefore, ifthe thickness of the silicon substrate is set to 3 μm or more, it ispractically possible to cause sufficient photoelectric conversion in thesemiconductor substrate SUB regarding light of any of R, G, and B.

Further, the n-type semiconductor substrate SUB in the secondconfiguration example has an impurity concentration gradient so that theconcentration increases from the first surface toward the semiconductorregion n1 on the second surface side. Specifically, a first impurityconcentration on the first surface side of the semiconductor substrateSUB becomes lower than a second impurity concentration of thesemiconductor region n1 (first impurity concentration<second impurityconcentration). Accordingly, in the n-type semiconductor substrate SUB,a potential of the semiconductor region n1 with high impurityconcentration becomes lower than a potential on the first surface sidewith low impurity concentration. Therefore, in the second configurationexample, it becomes easy for a charge to flow toward the semiconductorregion n1, because of a difference in the potentials from the firstsurface side of the semiconductor substrate SUB to the semiconductorregion n1, resulting in that a transfer omission in the photodiode PD issuppressed. Note that the impurity concentration of the semiconductorsubstrate SUB may also be rapidly changed stepwise in the thicknessdirection of the substrate, as long as it satisfies a condition that theimpurity concentration on the second surface side is higher than that onthe first surface side.

Note that in the second configuration example, the p-type semiconductorlayer 34 is formed on the first surface of the semiconductor substrateSUB, and the p-type semiconductor layer p+ is formed on the secondsurface of the semiconductor substrate SUB, so that the photodiode PDhas a p+np− structure. Accordingly, in the second configuration example,it is possible to suppress a dark current in the photodiode PD.

Further, the impurity concentration of the semiconductor region n1 ofthe photodiode PD and the impurity concentration of the semiconductorregion n2 of the storage diode SD are different to each other. Forexample, the impurity concentrations of the semiconductor regions n1 andn2 are respectively set so that a potential of the storage diode SD ispositioned between a potential of the photodiode PD and a potential ofthe floating diffusion part FD, when the first global switch transistorGS1 is at a low level.

Therefore, when the first global switch transistor GS1 is at a highlevel, the charge generated in the semiconductor substrate SUB flowsinto the semiconductor region n2 of the storage diode SD via thesemiconductor region n1, due to the difference in the potentials. Notethat the shield layer p2 as the insulation section exists between thesemiconductor region n2 of the storage diode SD and the semiconductorsubstrate SUB. For this reason, when the first global switch transistorGS1 is at a low level, the charge generated in the semiconductorsubstrate SUB is shielded by the shield layer p2, and thus never entersthe semiconductor region n2 of the storage diode SD.

Further, in order to insulate mutually adjacent pixels, at boundaries ofpixels PX, the p-type separating sections IS are formed. The separatingsections IS in the second configuration example are formed to reach thefirst surface from the second surface of the semiconductor substrateSUB. The separating section IS is, for example, a p-type well. Note thatthe separating section IS may also be one including a trench. Further,at a position among the storage diode SD, the separating section IS, andthe shield layer (p2), a p-type region 37 is formed. In like manner, ata position between the shield layer (p2) and the semiconductor substrateSUB, a p-type region 38 is formed, and at a position among theseparating section IS, the semiconductor substrate SUB, and thephotodiode PD, a p-type region 39 is formed. Note that the conductivitytype of the semiconductor described in the second configuration exampleis only one example.

The imaging device 12 b in the second configuration example can obtainnot only the operations and effects ((1) to (5)) of the firstconfiguration example, but also the following operations and effects.

If intense light is incident when the wiring layer MLY is positionedbetween the lightproof film of the lightproof section MS and thesemiconductor substrate SUB, there is a possibility that excess light isleaked to the storage diode SD from an extremely small gap between thelightproof film and the imaging plane, to cause the generation of falsesignal (smear).

On the other hand, in the imaging device 12 b in the secondconfiguration example, the wiring layer MLY is positioned on the rearsurface side of the incident surface, so that light is not directlyincident on the storage diode SD, and in addition to that, the incidentlight is subjected to the photoelectric conversion by the semiconductorsubstrate SUB. For this reason, in the imaging device 12 b, even if theintense light is incident, there is no chance that the light is leakedto the storage diode SD, so that it is possible to suppress the smearcaused by the leakage of light to the storage diode SD, resulting inthat the possibility of generation of the smear in the storage diode SDis significantly reduced.

<Third Configuration Example of Imaging Device>

Next, an imaging device 12 c in a third configuration example will bedescribed, as a modified example of the second configuration example.FIG. 13 is a diagram illustrating an example of pixel PX when seen froma side of a rear surface of a light receiving surface (second surface)in the imaging device 12 c in the third configuration example.

Hereinafter, a point of difference between the imaging device 12 c inthe third configuration example and the imaging device in the secondconfiguration example will be described. In the imaging device 12 c inthe third configuration example, an area of the photodiode PD is set tobe smaller than an area of the storage diode SD, on the rear surface ofthe light receiving surface (second surface). Accordingly, anarrangement interval of the first reset transistor RST1, the firstglobal switch transistor GS1, and the second global switch transistorGS2 becomes small, which enables to reduce the size of the pixel PX.Therefore, in the third configuration example, it becomes easy toincrease the number of pixels in the imaging device. Note that when therear surface irradiation type imaging device is employed, thephotoelectric conversion of incident light is performed in thesemiconductor substrate SUB as described above, so that no largeinfluence is exerted even if the size of the photodiode PD on the secondsurface side is reduced.

<Supplementary Items of Embodiments>

(Supplement 1): The imaging device in each of the first configurationexample to the third configuration example may also have a stackedstructure. For example, the imaging device 12 may also be configured bystacking a first substrate and a second substrate, and by electricallyconnecting the first substrate and the second substrate using aconnection portion MB such as a micro-bump, for example. By making theimaging device have the stacked structure, it is possible to integratecircuits within a small space, resulting in that it becomes easy toincrease the number of pixels in the imaging device.

As one example, it is also possible to arrange, on the first substrate,the photodiode PD, the first reset transistor RST1, the first globalswitch transistor GS1, the storage diode SD, the transfer transistor TX,the second global switch transistor GS2, the second reset transistorRST2, the amplifying transistor AMP, and the selection transistor SEL,as illustrated in FIG. 14(a). Further, it is also possible to arrange,on the second substrate (one example of signal processing substrate),the horizontal scanning part 33, the A/D conversion circuit, the CDScircuit and the like. Accordingly, signals in accordance with chargestransferred to the floating diffusion parts FD of the respective pixelsare processed in the second substrate.

Further, it is also possible to arrange, on the first substrate, thephotodiode PD, the first reset transistor RST1, the first global switchtransistor GS1, the storage diode SD, the transfer transistor TX, andthe second global switch transistor GS2, as illustrated in FIG. 14(b).Further, it is also possible to arrange, on the second substrate, thesecond reset transistor RST2, the amplifying transistor AMP, theselection transistor SEL, the vertical signal lines VL, the horizontalscanning part 33, the A/D conversion circuit, the CDS circuit and thelike.

(Supplement 2): The configuration of the rear surface irradiation typeimaging device including the storage section described in theaforementioned second configuration example can also be applied to acase where a pixel arrangement different from that of theabove-described embodiment is employed. For example, in an imagingdevice in which imaging pixels and focus detecting pixels are arrayed ina square lattice shape as illustrated in FIG. 15, a configuration of thefocus detecting pixel or the imaging pixel may also be set to one as inthe second configuration example (FIG. 9, for example).

(Supplement 3): The above-described configuration examples describe thecase where the center of optical axis of the microlens MLN of each pixelis aligned with the boundary between the lightproof section MS and theopening (photoelectric conversion section). However, in the presentinvention, it is also possible to design such that the center of opticalaxis of the microlens MLN of each of the respective pixels including thefirst pixel to the sixth pixel is positioned on the photoelectricconversion section side, relative to the boundary between the lightproofsection MS and the opening (photoelectric conversion section). Forexample, it is also possible to design such that the center of opticalaxis of the microlens MLN is positioned at a center of gravity of theopening.

(Supplement 4): In the above-described second configuration example, thep-type semiconductor layer 34 provided on the first surface of thesemiconductor substrate SUB may also be omitted.

(Supplement 5): The configuration example of the above-described imagingdevice is only one example of the present invention. For example, in theimaging device of the present invention, it is also possible to omit thefirst reset transistor RST1, and the second global switch transistor GS2from the pixel PX.

(Supplement 6): Although the above-described embodiments describe thedigital camera 1 in which the interchangeable lens 2 is mounted on thecamera body 3, as an example of imaging unit, the present invention canalso be applied to, for example, a lens integrated-type digital camera.Further, the imaging unit of the present invention may also be one whichis mounted on, for example, an electronic device having a camera module(for example, a smartphone, a mobile phone, a tablet type computer, andthe like).

(Supplement 7): Although the above-described embodiments describe a casewhere the imaging device 12 uses the color filters of primary colorsystem (RGB), it is also possible to use color filters of complementarycolor system (CMY).

The many features and advantages of the embodiments are apparent fromthe detailed specification and, thus, it is intended by the appendedclaims to cover all such features and advantages of the embodiments thatfall within the true spirit and scope thereof. Further, since numerousmodifications and changes will readily occur to those skilled in theart, it is not desired to limit the inventive embodiments to exactconstruction and operation illustrated and described, and accordinglyall suitable modifications and equivalents may be resorted to, fallingwithin the scope thereof.

The invention claimed is:
 1. An imaging device comprising: a firstsubstrate comprising: a photoelectric converter including (i) a firstsemiconductor that is of a first conductivity type and has (a) a firstsurface on which light is incident and (b) a second surface on anopposite side of the first surface, and (ii) a second semiconductor thatis of a second conductivity type different from the first conductivitytype and is formed between the first and second surfaces; and a transfergate that is arranged on the second surface side of the secondsemiconductor and transfers a charge stored in the second semiconductor;and a second substrate comprising an amplifying transistor, the secondsemiconductor having an impurity concentration gradient from the firstsurface side of the second semiconductor toward the second surface side,and an impurity concentration on the second surface side of the secondsemiconductor being higher than an impurity concentration of the secondsemiconductor on the first surface side.
 2. The imaging device accordingto claim 1, further comprising a storage diode storing the charge withinthe second semiconductor.
 3. The imaging device according to claim 2,the storage diode comprising a semiconductor that is of the secondconductivity type and has an impurity concentration higher than theimpurity concentration on the second surface side of the secondsemiconductor.
 4. The imaging device according to claim 3, furthercomprising: an insulator comprising a semiconductor that is of the firstconductivity type and prevents the charge in the second semiconductorfrom entering the storage diode.
 5. The imaging device according toclaim 2, further comprising: a first pixel and a second pixel adjacentto the first pixel, each of the first pixel and the second pixelincluding a said photoelectric converter, a said storage diode, and asaid transfer gate; and a separator that separates the photoelectricconverter of the first pixel and the photoelectric converter of thesecond pixel.
 6. The imaging device according to claim 5, the separatorcomprising a semiconductor of the first conductivity type.
 7. Theimaging device according to claim 5, the separator having a trench. 8.The imaging device according to claim 5, the first pixel and the secondpixel further including, respectively, a first pupil-division lightprooffilm and a second pupil-division lightproof film that enable thephotoelectric converters of the first and second pixels to convertpupil-divided light fluxes into charges and thereby output the chargesas phase difference information, and the photoelectric converter of thefirst pixel, the first pupil-division lightproof film, the secondpupil-division lightproof film, and the photoelectric converter of thesecond pixel being arranged in this order in a predetermined direction.9. The imaging device according to claim 5, the first pixel furtherincluding a first lightproof film that shields the storage diode of thefirst pixel from light; and the second pixel further including a secondlightproof film that shields the storage diode of the second pixel fromlight.
 10. An imaging unit, comprising: an infrared cut filter; and theimaging device according to claim 1, light passed through the infraredcut filter entering the imaging device.
 11. The imaging unit accordingto claim 10, a thickness of the photoelectric converter in a directionorthogonal to the first surface being 3 μm or more.
 12. The imagingdevice according to claim 1, the second substrate further a comprisingselection transistor connected to a source of the amplifying transistor.